Plastic containers for food and beverages from polyethyleneterephthalate (PET), polypropylene (PP) or polyethylene (PE) are long known and are mostly produced in stretch blow molding processes.
It is also known to apply a barrier coating on such containers in order to reduce the permeation of gases, especially oxygen or carbon dioxide into or out of the container, thereby improving the shelf life of the packed goods.
For example, WO 03/037969 A1, GB 879595, DE 10153210 and DE 10207592 A1 describe the use of polyvinyl alcohol as gas barrier on PET bottles with an additional top coat comprising polyvinyl butyral to improve the water resistance of the barrier coating. Such multilayer coatings show a good barrier performance against oxygen and carbon dioxide, scratch resistance and are recyclable after mechanically destroying the top layer due the to the water solubility of the barrier coating.
Most plastic bottles for example used for soft drinks are produced by injection stretch blow molding from so called preforms. In such blowing processes, the preform is expanded to more than 10 times of its original volume resulting in a significant thinning of any coating layered on the surface of the preform. In order to prevent the degradation or cracks of the barrier coating during the stretch blow process, the prior art suggests several film building polymers for the top coating.
In this respect, GB 2337470 A1 discloses a method for coating a PET preform for bottles with a barrier coating based on PVA and protection of the barrier coated preform by applying a second polymeric material. As second polymeric material, polyester like PET and polycarbonates are suggested. This publication describes furthermore chemical or physical pre-treatments of the surface of the substrate prior to application of the barrier coating.
A similar technique is disclosed by WO 2004/089624, where containers for food or manufactured goods from PET or polyolefins are first coated with a blend of at least two polymers including PVA, polyamines, polyvinylimines, polyacrylic acids etc. and subsequently with a protective coating of polyurethanes, PVC or polyacrylates. Optionally and prior to the barrier coating, the substrate may be pre-treated by plasma, flames, chlorine, fluorine or chemical etching. Top coating polyvinyl alcohol as quite polar polymer with the polymers as proposed by this publication will result in mechanically and chemically unstable layers.
Many of the described plastic containers are used for end consumer products like food (ketchup, mayonnaise, jam) or personal care (shampoo, body lotion). There is a constant complaint of the customers of such goods that the plastic (bottles) can not be emptied completely and a part of the content of the container/bottles is wasted. Furthermore, customers and manufacturers would like to prolong the shelf-life of the packed goods without changing the thickness or the composition of the plastic material of the container.
Accordingly there is a need to improve the shelf-life of the packed goods and in addition the emptying behavior of the container at the same time.